The present invention relates generally to drilling and drillstring equipment for oil and gas drilling, water well drilling, geothermal drilling, etc.
Most traditional drillstrings are constructed of straight sections of rigid pipe (i.e., ‘rigid tubulars’) interconnected (i.e., joined) by threaded joints. The pipe is typically manufactured with a thick wall section to allow it to convey large mechanical loads.
Coiled tubing is also used for drillstring tubulars. Its advantage is it can be transported to the drill site in long lengths (wrapped around a large spool) and readily deployed into the well. It is typically manufactured with a thinner wall than rigid pipe because it must be transported by wrapping the tubing around a spool (typical spool diameter ranges from 4-8 ft). It is deployed into the well by un-coiling it from the spool into a linear section, and then bending it over a gooseneck and down into the well. Coiled tubing typically has a wall thickness of 3/32- 3/16 inches thick, and outer diameter about 2-3 inches (e.g., 2.5 inches). Coiled tubing has material limitations in how tightly it can be wound on the spool. It also requires large forces to deploy it from the wound condition.
Traditional thick-walled jointed pipe offers the benefit of a tubular with greater strength; while thin-walled coiled tubing offers the benefit of rapid deployment.
The segmented coiled tubing concept of the present invention is a system that provides the benefits of both jointed pipe and coiled tubing. It eliminates the bending operation during unwinding, it can self-assemble, and it acts like rigid pipe once assembled.
Against this background, the present invention was developed.